Organic materials, such as pitch, stickies, and tackles, are major obstacles in paper manufacturing because these materials when liberated during a papermaking process can become both undesirable components of papermaking furnishes and troublesome to the mill equipment, e.g. preventing proper operation of mechanical parts when these materials deposit on the mechanical parts. White pitch is a particular obstacle in the manufacture of paper and tissue using recycled fiber (mixed office waste, old corrugated containers, old newsprint) and coated broke. For paper grades, these non-polar, tacky contaminants, when liberated during processing repulping, can become both undesirable components of papermaking furnishes and troublesome deposits on the mill equipment, e.g. wires of the tissue machine.
Stickies and tackles are organic materials that do not have precise definitions; they are tacky substances contained in the pulp and process water system that deposit on paper/tissue machine clothing, cylinders, and/or rolls. They vary in chemical structure: natural wood pitch consists of fatty acids, fatty esters and rosin acids, while stickies and white pitch originating from synthetic additives (adhesives, coating binders, printing ink) contain styrene butadiene rubber, ethylene vinyl acetate, polyvinyl acetate, polyvinyl acrylate, polyvinyl butyral, polybutadiene, wax, alkyd resins, polyol acrylates, etc. However, they all are hydrophobic materials that do not have a strong affinity to metal surfaces that creates a problem in monitoring such microparticles (micro stickies are those that can pass the 0.10-0.15 mm screening slots) using a of conventional quartz crystal microbalance (QCM).
U.S. Patent Application Publication No. 2006/0281191 (Duggirala et al., assigned to Nalco Company) discloses using a quartz crystal microbalance (QCM) in monitoring of organic deposits. The disclosed method is not universal and cannot be used in a special case of highly hydrophobic microstickies because they do not accumulate on the metal surface.
A publication by Tsuji et al. (2006) claims a new method for measuring microstickies in deinked pulp processes using a QCM-D (quartz crystal microbalance with dissipation monitoring) technique. The samples were taken at the inlet and the outlet of flotation cells for white water in a deinking mill. The adsorption behavior of dissolved and colloidal substances (DCS) in white water onto the surfaces (hydrophilic Au and hydrophobic polystyrene) was monitored. However, the published results demonstrated a very poor response of the sensor, orders of magnitude lower than that observed when the technique proposed in the parent application. Tsuji et al. does not indicate whether the observed changes are caused by microstickies.
Deposition of organic materials on the surface of a quartz crystal microbalance sensor is known. However, due to the low affinity of a standard surface to hydrophobic organic materials, the rate of deposition is normally low.
Coating of the QCM surface to affect the rate of deposition, generally, is a known idea. Moreover, a polymer coating composition including an epoxy resin (the preferred coating in the parent application) was described, though with a different aim. However, the special method of coating developed here and the application of a specially designed polymer and a class of polymers, effectively providing a sensitizing coating for stickies monitoring using QCM is now identified.
Additionally, the hydrophobic materials in pulp slurries (pitch in virgin pulp, stickies in recycled furnish) are known to have relatively low surface energy; for stickies it is in the range 30-45 dynes/cm2, and, for example, the tack for pressure-sensitive adhesives (PSA) depends on the surface energy. Surface energy quantifies the disruption of intermolecular bonds that occurs when a surface is created. The surface energy may be defined as the excess energy at the surface of a material compared to the bulk
An efficacious and enhanced method of monitoring the deposition of organic materials is thus desired. Furthermore, a method of monitoring the effectiveness of inhibitors that prevent/reduce deposition of organic materials in a papermaking process is also desired. Even further, a method of measuring microstickies in deinked pulp processes using a QCM technique is ultimately desired.